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Old 07-21-2011, 05:40 PM   #1
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Distribution: Red Hat Enterprise Linux 5 x86_64
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XDMCP tunneling in Xming portable PuTTY SSH connection

For over a year I have been using Xming portable PuTTY (7-5-0-18) to connect FROM a computer running M$ Windows XP Pro TO a RHEL v5.6 computer. I have been using Xming (7-5-0-17) on the XP computer in order to run a gnome GUI session. My network card connections and ports are 1 GB. In the past the XP computer and RHEL computer were connected on a LAN and the gnome GUI windowing was very fast - virtually instantaneous. The RHEL computer was recently moved to a different building and the XP computer and RHEL computer are connected through a WAN. Now the gnome GUI windowing seems like it runs at 100 MB on a good day and many times at 10 MB. I was instructed by our IT group that connecting using a MS Windows Remote Desktop Connection would make the gnome GUI windows faster. The network ports are not the problem - they are all 1 GB ports, have been checked, and are functioning correctly. I think the speed bottleneck is that the connection is now going through a WAN and the gnome session start up errors.

When I start the gnome GUI session, several lines of errors appear. This is true when the 2 computers were connected through the LAN, and now the WAN. I believe they're the same set of errors. A suggestion from RHEL support is to "connect to your server using XDMCP instead of SSH". I don't really know what it means to connect to my server using XDMCP (like how?) and from what I've been reading, I don't want to connect to the RHEL server using straight XDMCP, but rather establish an XDMCP tunnel through the SSH connection for security reasons. Am I way off base here?

Here is how I have been connecting:
Invoke Xming on the XP computer. Start an Xming portable PuTTY X terminal window on the XP computer. For the connection I am using SSH (port 22), have X11 forwarding enabled, and have the X display location set at localhost:0.0. After logging in to the RHEL server, I type gnome-session. The gnome GUI session opens its windows, etc, in the Xming window.

This is what I've tried:
Most recently I went through the steps at I have added the line -A RH-Firewall-1-INPUT -p udp -m udp --dport 177 -j ACCEPT to my /etc/sysconfig/iptables and restarted the service. I also went through the steps in the Xming portable PuTTY help instructions for using port forwarding in SSH. In the Tunnels window I added port 3110 to Source port and specified the Destination as 123.456.78.910:177. Apparently I didn't mess anything up as I can still start a gnome GUI session in the Xming window. However I have no idea if I have actually established an XDMCP Tunnel in the SSH connection and am using it.

BTW I am now using Xming portable PuTTY version 7-5-0-39 and Xming version 7-5-0-38.

Several questions:
If I correctly establish the XDMCP tunnel in the SSH connection, can I expect to have 1 GB speed between the XP and RHEL computers?
Is this type of connection considered to be a "Remote Desktop Connection"?
How do I determine if I have established and am actually using the XDMCP tunnel through the SSH connection and not just only the SSH connection as before?

Any insights, instructions, and/or helpful URLs would be greatly appreciated.



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